wpa_supplicant.conf automatic WEP key
 

I am editing wpa_supplicant.conf

I have been trying to no avail to setup an automatic WEP key.

I know how to use manual setttings such as:
web_key0="...."

but this one is automatic. how do I achieve this?

In windows XP I just click the "The Key is provided for me automatically" tick box.